This invention relates to an oil filter for an internal combustion engine.
A filter of this type is disclosed in EP 0 492 627. The collecting space is closed so that liquid penetrating into it cannot flow off to the outside.
The publication WO 97/16234 discloses a liquid filter for cleaning oil or fuel, which is flanged onto an engine block of an internal combustion engine. Arranged in the filter housing, which consists of plastic, is a cylindrical filter body whose unfiltered side is acted upon by contaminated liquid which is supplied via a feed channel. The outflow space of the filter body is connected to a return channel via which the cleaned liquid can be taken away out of the filter housing. The feed channel surrounds the return channel annularly, the outer wall of the feed channel being formed by the outer wall of the filter housing. The end-side connections of the feed and return channels are inserted via seals into receptacles on the engine block.
The liquid to be cleaned is guided through the feed channel to the filter body under positive pressure. There is the risk here of leakages occurring in the region of the connection of the filter housing to the engine block, for example as a consequence of material fatigue of the seals, so that unfiltered liquid passes to the outside and can cause contamination or flows inwardly into the return channel and mixes with the liquid which has already been cleaned. In order to reduce this risk, the seals have to be made from very high quality and expensive materials. In addition, even small leakages cause a sharp drop in pressure which means that the minimum pressure required for the filtration cannot be applied and the filtration cannot be carried out.
Because of the large external radius of the feed channel, a large amount of sealing material is needed in order to seal the feed channel, and because of this, in addition to the increased costs, the risk of there being a leakage place also increases and frequent maintenance intervals are required.
The invention is based on the problem of designing an operationally reliable and low-maintenance, plastic liquid filter of the generic type at low cost, even in the case in which , because of material and/or manufacturing errors, liquid under a high pressure unintentionally penetrates into the collecting space in a greater volume than this space is able to absorb without an increase in pressure. In addition, the filter according to the generic type is to be designed in a form which makes it possible for additional functional parts, such as, in particular, a cooler for the liquid to be filtered, and also pressure sensors to be integrated in a structurally efficient manner.
This problem is already solved in principle according to this invention.
The feed channel and the return channel are situated in a collecting space having a safety wall which is part of the filter housing and surrounds the feed channel and the return channel radially. If the liquid filter is connected to a connecting flange, for example an engine block of an internal combustion engine, the safety in the event of leaky seals is increased because both the inflowing unfiltered liquid and also the outflowing clean liquid are sealed off twice from the environment: within the feed and the return channels and, in addition, within the collecting space whose wall can be connected in a liquid-tight manner to the connecting flange at low cost. In addition, liquid penetrating into the collecting space can flow off through the outlet provided there, as a result of which an undesirably high pressure in the collecting space is reliably avoided. The pressure in the collecting space is restricted to the pressure at its outflow opening.
The collecting space can be configured to atmospheric pressure. The positive pressure in the flow of liquid which is supplied and taken away is completely absorbed by the feed and return channels, respectively. The collecting space remains unaffected by this, and acts as a safety reservoir in the event of leakages occurring. This means that the seal between the safety wall and the connecting flange is not required to be of more exacting quality, that is to say, a simple O-ring seal can be used, for example.
The plastic filter housing can be manufactured by injection moulding in a cast with sufficient dimensional accuracy that finishing is no longer required. In addition, a considerable advantage in terms of weight is obtained. The channels which are formed in the filter housing can be designed such that they have relatively thick walls in order to be able to absorb the pressures prevailing in the liquid; at the same time, the safety wall can be designed such that it has thin walls, since there is no positive pressure in the collecting space.
The connections of the feed channel and of the return channel are advantageously provided with a radial seal in order to obtain, a pressure- and liquid-tight seal between the filter housing and the connecting flange. Retaining forces acting in the axial direction are essentially transmitted via the safety wall of the collecting space, which is free of excess pressure, and in particular via fastening domes which are of reinforced design and in which metal bushings are expediently accommodated, so that the channels are relieved of high axial forces and undesired creeping behaviour of the plastic in the region of the channels is avoided.
The radial seals are preferably of spherical design in order to be able to compensate for axial tolerances.
Because of the connection of the collecting space to a discharge channel, liquid which has emerged into the collecting space, for example from the feed channel or the return channel via leaky radial seals, is conducted away out of the collecting space via the said discharge channel, and, in particular, into the oil sump of the internal combustion engine. As already set out further above, this prevents the collecting space from filling up with liquid and a positive pressure from building up in the collecting space. The discharge channel runs in the connecting flange and is connected to the collecting space via a recess in the connecting flange.
Furthermore, a pressure relief valve can be provided in the collecting space, which pressure relief valve is acted upon by the pressure on the clean side of the filter and when a limiting pressure is exceeded, opens towards the collecting space and thereby causes the pressure to be relieved. The liquid which has emerged into the collecting space is conducted away again out of the collecting space via the discharge channel.
The end sides of the channels respectively each end at a different axial distance, as does a housing receptacle into which the pressure relief valve can be inserted. Assembly is hereby facilitated by the filter housing being placed onto the connecting flange with an approximately uniform, axial assembly force, and first of all the component protruding the furthest, and then the components protruding to a lesser extent, are successively inserted into corresponding receptacles in the connecting flange. This also prevents the filter housing from tilting during assembly.